Therapeutic proteins are currently used to treat a wide variety of diseases. Therapeutic proteins can range in size from small synthetic polypeptides that are less than 50 amino acids in size to larger recombinant proteins, including fusion proteins, as well as monoclonal antibodies or fragments thereof. Typically, therapeutic proteins are larger than non-protein medications and, therefore, pose unique problems in determining their concentrations in tissue, serum and plasma. However, the pharmacokinetic aspects of a therapeutic protein must be determined during clinical testing and after in order to assess safety and efficacy. Usually, therapeutic protein concentration is detected using immunochemical techniques which employ such detection methods as colorimetry, flourimetry, or luminescence. However, immunochemical techniques merely provide non-selective results.
Additionally, mammals, including humans, naturally produce endogenous proteins that can be used as biomarkers for certain diseases or to predict response to certain therapeutics. For instance, natural production of certain cytokines by a mammal may be associated with diseases and disorders as well as inflammation. Additionally, certain tumour associated proteins can be produced by a mammal suffering from a particular type of cancer. Furthermore, mammals may have immunogenic responses to therapeutics, including small molecules, polypeptides and antibodies; therefore, producing endogenous antibodies against therapeutics administered to the mammal. Thus, a robust and sensitive method for determining therapeutic and/or endogenous protein from plasma is needed.